Parasitic Resistance in capacitors/inductors

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In summary, the conversation discusses finding the frequencies at which the current amplitude through a parasitic resistance is equal to the current amplitude through a capacitor and the amplitudes of the currents through the resistor and capacitor are equal. The formula for capacitive reactance is mentioned and it is noted that the approach may differ if an inductor is used instead, depending on how losses are modeled.
  • #1
dudforreal
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Homework Statement
A 82 nF capacitor has a parasitic parallel resistance Rp = 600 kΩ.
If a voltage V = Vmsin(ωt) is applied, as shown in the diagram, find the frequencies at which:
1. The current amplitude through the parasitic resistance is 1% of the current amplitude
through the capacitor.
2. The amplitudes of the currents through the resistor and the capacitor are equal.


The attempt at a solution

I don't even know where to start with the question and I do not know what equations are needed to get the answer. Any help from people would be great.
 
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  • #2
The current is equal when the reactance of the capacitance is equal to that of the (equivalent) resistance.

Do you know the formula for capacitive reactance.
 
  • #3
ok thanks i got the answer but how would you go about it if it was an inductor instead?
 
  • #4
dudforreal said:
ok thanks i got the answer but how would you go about it if it was an inductor instead?

That would depend upon whether the inductor losses were modeled by a series resistance or an equivalent parallel resistance. Copper losses are usually modeled with a series resistance whereas core loses are usually modeled with an equivalent parallel resistance.
 
  • #5
ok thanks :smile:
 

FAQ: Parasitic Resistance in capacitors/inductors

1. What causes parasitic resistance in capacitors and inductors?

Parasitic resistance in capacitors and inductors is caused by the inherent resistive properties of the materials used in their construction, as well as the physical design and layout of the components. In capacitors, parasitic resistance is often due to the leads and connections used to attach the plates to the rest of the circuit. In inductors, parasitic resistance can be caused by the wire used in the coil, as well as any inter-turn spacing or proximity to other components.

2. How does parasitic resistance affect the performance of capacitors and inductors?

Parasitic resistance can significantly degrade the performance of capacitors and inductors. It can increase the equivalent series resistance (ESR), which can lead to increased power losses, decreased efficiency, and reduced bandwidth. In some cases, parasitic resistance can also cause unwanted coupling between components, resulting in crosstalk and signal interference.

3. Can parasitic resistance be reduced or eliminated in capacitors and inductors?

While it is not possible to completely eliminate parasitic resistance, it can be reduced through careful design and selection of materials. For example, using lower resistance materials such as copper instead of aluminum can help reduce parasitic resistance in capacitors. In inductors, using thicker wire and reducing inter-turn spacing can also help minimize parasitic resistance.

4. How can parasitic resistance be measured in capacitors and inductors?

Parasitic resistance in capacitors and inductors can be measured using a variety of techniques, such as impedance analysis or network analysis. These methods involve applying a small signal to the component and measuring the resulting impedance. The higher the impedance, the higher the parasitic resistance. Specialized test equipment, such as an LCR meter, can also be used to measure parasitic resistance.

5. Are there any techniques for mitigating the effects of parasitic resistance in capacitors and inductors?

There are several techniques that can be used to mitigate the effects of parasitic resistance in capacitors and inductors. These include using higher quality materials, such as low-ESR capacitors and high-conductivity wire for inductors. Another approach is to use multiple smaller capacitors or inductors in parallel instead of a single large one, as this can help distribute the parasitic resistance and reduce its overall impact on performance.

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